The present invention relates to a green tire building apparatus for use in a tire production process.
As an apparatus for building a green tire, there has been conventionally known, for example, a single-stage building apparatus as shown in FIG. 4. The apparatus shown in FIG. 4 is symmetrical with respect to a vertical center line of a shaping drum, and therefore only a left half of the apparatus is shown in the figure for the sake of simplicity. In FIG. 4, indicated at 1 is a rubber former, and at 2 a turned-up bladder. When the bladder 2 is not inflated and a bead locking mechanism is not actuated, an outer surface of the bladder 2 is in the form of a cylinder having substantially the same radius as a cylinder formed by an outer surface of the rubber former 1.
An end of the rubber former 1 is fixedly held by clamp rings 3, 3'. An inner end 12 of the bladder 2 and an outer end thereof are fixed respectively neighboring the end of the rubber former 1. A rubber solid band 4' is integrally formed with the outer end of the bladder 2. Another rubber solid band 4 is also formed integrally with the bladder 2 near the inner end thereof. Both rubber solid bands 4, 4' are fitted in respective recessed portions 6 formed in outer surfaces of a plurality of metal segments 5 arranged in a circumferential direction of the shaping drum. The metal segments 5 collectively form an annular body. An annular rubber bag 7 is provided inside the metal segments in contact with an inner surface of the annular body formed by the metal segments 5, Indicated at 8 is a support for the bladder 2.
In this apparatus, a carcass 9 is formed by winding tire components such as a ply and a chafer onto the rubber former 1. A bead 10 provided with or without an apex is set in a specified position on the carcass 9. In this state, when the rubber bag 7 is inflated with the air supplied to the inside thereof, a state shown in FIG. 4 can be obtained. More specifically, the rubber bag 7 pushes the metal segments 5 outward, i.e., in a direction of an arrow A in FIG. 4, expanding radii of the rubber solid bands 4, 4'. In addition, a portion 9a of the carcass 9 in contact with the bead 10 is pushed up against an inner circumferential surface of the bead 10 by the inflated rubber bag 7, and thereby the bead 10 is locked in the portion 9a. This mechanism is referred to as a bead locking mechanism hereinafter.
In the above state, the bladder 2 is inflated with the air supplied to the inside thereof, and a side portion 9b of the carcass 9 is turned up around the bead 10 by the inflated bladder 2. This mechanism is referred to as a carcass turn-up mechanism hereinafter. Further, the clamp rings 3, 3', the bead locking mechanism, and the carcass turn-up mechanism are moved by a predetermined distance in an axial direction of the shaping drum to a right half of the apparatus, i.e., in a direction of an arrow B while inflating the rubber former 1. Thereby, the carcass 9 is shaped in the form of a toroid. A green tire can be completely built by applying a breaker and a tread assembly to the toroidal carcass.
However, in the above apparatus, the metal segments 5 are moved outward by the inflation of the rubber bag 7, therefore there is a limit in the pressure generated in the rubber bag 7. Accordingly, the carcass portion 9a locks the bead 10 in contact therewith with insufficient restraint. With the bead 10 locked with the insufficient restraint by the carcass portion 9a, when pulled during a tire shaping operation on the rubber former 1, the carcass portion 9a is liable to dislocate relative to the bead 10 in the axial direction of the shaping drum. Consequently, cord paths become out of place, causing uniformity of the tire to degrade.
Further, the rubber bag 7 liable to deform is used in this apparatus. Accordingly, a center of the bead 10 is liable to dislocate from that of the shaping drum, resulting in eccentricity. This is also a large factor contributing to degradation of the uniformity.
Moreover, in the above apparatus, the rubber solid bands 4, 4' are integrally formed with the bladder 2. Accordingly, it is difficult to fabricate the bladder 2 and to assemble the bladder 2 into the apparatus. Furthermore, in the case where the bladder 2 is punctured, the rubber bands have to be replaced with new ones together with the bladder, wasting the still usable rubber bands.